As wheeled vehicles such as trucks have increased in size, weight and load carrying capacity it has become increasingly important for the vehicle driver to have knowledge of the effectiveness of the brake members during the braking process and of the state of readiness of the braking components particularly in terms of temperature and wear at all times. In a typical vehicle braking system some type of friction element such as a brakeshoe in a drum brake system or a brake pad in a disc brake system is adapted to be moved against a rotating brake drum or disc brake rotor during the braking process. It should be noted that the subject invention is applicable equally to drum brake systems or to disc brake systems. Accordingly, for convenience and to avoid unnecessary repetition this description will refer to drum brake shoes and disc brake pads collectively as brake blocks and will refer to brake drums and rotors collectively as brake drums. In braking systems it has been determined that one indication of the effectiveness of the braking system during the braking process is the temperature at the interface of the brake block friction face and the brake drum friction surface during the braking application. Additionally, it has been determined that the readiness of the braking system may be determined by the thickness of the friction material in the brakeblock and by the steady state temperature of the friction material when the brakes are not being applied.
A major problem in attempting to ascertain the temperature at the brake block-brake drum interface resides in the fact that the temperature at spaced discrete points across the width of the friction material face varies considerably during the braking operation. Such a fact has been confirmed by placing the junctions of thermocouples at spaced points across the face of the friction material of a brake block . Because the temperature indications vary so extensively the information provided by conventional thermocouples at the interface have been relatively useless. In analyzing the braking components during the braking process it has been found that the face of the brake block friction material does not always contact the brake drum uniformly across the width of the friction face because of thermally induced distortion of the brake drum friction surface and because of uneven wear of the brake block friction surface. Consequently, it has become necessary to provide a temperature measuring device for use at the interface of a brake block and a brake drum which will provide an accurate indication of interface temperature despite thermal distortion of the brake drum and uneven wear of the friction element surface.
The subject invention provides a junction type thermal measuring device adapted to be affixed to the friction element of a brake block having one element that extends across a substantial portion of the brake block width and includes a working face that contacts a brake drum friction surface across a substantial portion of its width such that the device acts like an infinite number of thermocouples which are constantly monitoring the interface temperature between the brake block and the brake drum.